Define spark ignition, auto ignition, pre ignition, and surface ignition.

Define spark ignition, auto ignition, pre ignition, and surface ignition. 
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1 Answer

Answer :

1. Spark ignition: The term spark-ignition is ignition of charge (the air-fuel mixture) by a spark across electrodes of a spark plug. 

2. Auto ignition: It is spontaneous ignition of fuel: air mixture when introduced into the combustion chamber of an I.C. engine, as a result either of glowing carbon in the chamber or of the heat of compression. 

3. Pre-ignition: Pre-ignition is the ignition of the homogeneous mixture in the cylinder, before the timed ignition spark occurs, caused by the local overheating of the combustible mixture. Pre ignition is initiated by some overheated projecting part such as the sparking plug electrodes, exhaust valve head, metal corners in the combustion chamber, carbon deposits etc. 

4. Surface ignition: Surface ignition is the ignition of the fuel-air mixture by a hot spot on the combustion chamber walls such as on overheated valve or spark plug or glowing combustion chamber i.e. any means other than the normal spark discharge. Due to surface ignition a turbulent flame develop at each surface ignition locations and start propagates across the chamber in an analogous manner to what occurs in normal knock. 
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